The major aim of the proposed research is to characterize the mononuclear cells found in or around human breast cancers, through the use of monoclonal antibodies reactive with T cell populations, B cells, NK cells and monocytes. We will routinely study the cells in frozen tissue sections of primary breast tumors, using immunofluorescence and immunoperoxidase techniques. When sufficient tissue is available, suspensions will be prepared from the tumor site and the mononuclear cells studied for reactivity with various monoclonal antibodies by immunofluorescence and by flow cytometry on a fluorescence activated cell sorter; in addition, the cells will be studied for surface Ig, sheep erythrocyte rosetting and C3 and Fc receptors. Parallel studies will be carried out in some cases with peripheral blood cells, lymph node cells or with cells obtained from pleural fluid or ascites of patients with metastases. Attempts will be made to propagate T cells in vitro, starting with suspensions prepared from tumor sites or draining lymph nodes; the propagated cells will be studied for reactivity to antigens present in the tumor and other tissues and in established cell lines of breast and other tissues. Suspensions of tumor cells will be prepared and examined for surface Ig and used to determine if the patients have circulating antibodies or cell mediated reactivity directed against surface antigens. In all cases we will study the breast tumor histologically to classify the tumor and to assess pathologic features that are thought to correlate with prognosis. The nature, intensity and distribution of mononuclear and other inflammatory cells will be examined in regular histologic preparations and in one micron sections prepared from Epon embedded material. Immunofluorescence studies will be performed to determine estrogen receptor activity. The patients will be assessed for clinical features that correlate with prognosis and followed for evidence of recurrence or metastases.